1. Field of the Invention
This invention relates to methods of processing a substrate, and more specifically, to a chemical mechanical scrubbing process using Standard Clean 1 (SC1) for cleaning, for example, semiconductor wafers, including bare silicon wafers and processed and partially processed semiconductor substrates.
2. Background Information
In the manufacture of semiconductor devices, the surface of semiconductor wafers must be cleaned of wafer contaminants. If not removed, wafer contaminants may affect device performance characteristics and may cause device failure to occur at faster rates than usual.
A scrubber that scrubs a wafer on either one or both sides may be used to remove wafer contaminants. The type of cleaning solution (solution) used in the scrubber may depend upon the type of contaminants to be removed, the particular type of wafer to be scrubbed, and/or the particular manufacturer's preferred method for cleaning. For example, some manufacturers require a low level of contamination and may use a chemical solution for scrubbing, while other manufacturers have a higher contamination tolerance (i.e. less contamination need be removed) and may use only water for scrubbing.
Double sided scrubbers that use soft sponge like (e.g., PVA) brushes to simultaneously clean both sides of the wafer are widely used for post CMP (chemical mechanical planarization) cleaning, cleaning of silicon wafers and general fab cleaning. The effectiveness of scrubbing wafers with soft brushes to remove surface defects has been demonstrated in both research and production. The best cleaning performance is achieved when the surface state of the incoming wafer is hydrophilic. The wafer must be uniformly wetted with water while being scrubbed by the brush. The particles which are being dislodged from the wafer surface by the brush then become suspended in the film of water which covers the wafer surface. This particle-laden film is then displaced with freshly delivered, clean DI water. In this way, the particles are removed from the wafer.
If the surface of the wafer (or isolated areas on the wafer surface) is hydrophobic and, therefore, can not be uniformly wetted, the particles will remain adhered to the surface of the wafer. Particles will also deposit onto the hydrophobic wafer surface from the PVA brush. Therefore, it is required, for successful removal of surface contaminants by brush scrubbing, that the surface of the wafer is hydrophilic. This is the case for three widely employed CMP applications: CMP of interlevel dielectric, pre-metal dielectric and Tungsten (W) CMP for the definition of the interconnect structure. In these applications, the surfaces of the wafers after polishing are hydrophilic.
In the case of CMP of prime silicon or polysilicon, the surface after polishing may be hydrophobic. (A hydrophobic surface state is also characteristic of thermally grown silicon dioxide, as grown epitaxial silicon and prime silicon which has been stripped of its native or passivating oxide.) In these cases, the surface must be converted from hydrophobic to hydrophilic for successful removal of surface contaminants by brush scrubbing. One way to perform this conversion is to use SC1 chemistry.
Standard Clean 1 (SC1) is a well-known chemical combination that is used to clean bare silicon or a silicon wafer with thermally grown or deposited oxide. SC1 consists of ammonium hydroxide (NH.sub.4 OH), peroxide (H.sub.2 O.sub.2) and water (H.sub.2 O). An SC1 cleaning cycle is designed to promote oxidation and dissolution of organic impurities on the substrates in the solution of NH.sub.4 OH, H.sub.2 O.sub.2 and H.sub.2 O at a temperature of approximately 75.degree. C. to 80.degree. C. For one description of SC1 chemical cleaning, see W. Kern, "Hydrogen Peroxide Solutions for Silicon Wafer Cleaning," RCA Engineer, vol. 28-343, July/August 1983, pgs. 99-105.
Typically, to convert a hydrophobic surface of silicon or polysilicon to a hydrophilic surface, the substrates are dunked into a bath, separate from the scrubber, and then withdrawn from the bath and placed into a scrubber for cleaning. Thus, a separate piece of equipment is required for the conversion. What is desired is a way to allow substrates to go directly to the scrubber without having to use a separate piece of equipment such as a wet bath. A wet bath typically uses large volumes of water and chemicals and may become contaminated with repeated exposure to "dirty" wafers. It is also more difficult to control the chemical reaction at the wafer surface in a bath containing 50-100 wafers than in a single wafer system with the ability to deliver small amounts of fresh chemicals to each and every wafer.
The present invention provides for converting the surface of a semiconductor substrate in situ using an SC1 chemistry in a scrubber in such a way as to be compatible with the PVA brush material. The present invention provides for changing the surface state at the same time as mechanical brush cleaning. In this way, the use of additional equipment to convert the substrate surface from hydrophobic to hydrophilic is not necessary.